1. Field of Invention
The present disclosure relates to an SDPF (SCR on Diesel Particular Filter), which can prevent the NH3 oxidation reaction by a precious metal catalyst because an SCR catalyst layer and a precious metal catalyst layer are separated, and a method for producing the same.
2. Description of Related Art
In SDPF (SCR on Diesel Particular Filter), an SCR (Selective Catalytic Reduction) catalyst (Generally, Cu-zeolite, Fe-zeolite) is coated on a porous DPF (Diesel Particular Filter), and NOx in NH3 and exhaust gas supplied from the whole SDPF is reacted on the SCR catalyst and is purified to water and N2.
Further, because the SDPF functions as a filter, it collects soot (PM, Particulate Materials) in exhaust gas like DPF, and increase the exhaust gas temperature through post injection of a diesel engine resulting to oxidizing/removing the soot collected on the SDPF.
Now, the SDPF is classified to passive type and active type. The passive type is LNT+SDPF type, and when NOx collected in LNT is subjected to DeNOx process by post injection, NH3 is produced as a byproduct, and the NH3 and excess NOx in the exhaust gas are purified to NO2 in the SDPF.
The active type is equipped with an urea (urea water) injector on the whole SDPF and provides urea, and NH3 vaporized from the UREA is reacted with NOx in the SDPF and purified to N2. And, both passive and active types collect soot as SDPF's own function, increase the exhaust gas temperature by periodical post injection of an engine, and oxidize/burn the soot collected in the filter.
When increasing the exhaust gas temperature or producing NH3 by the 2nd jet, the 2nd EM (HC, CO and the like) is optionally generated. In the existing system (DOC+DPF or LNT+DPF), the 2nd EM, optionally generated by a catalyst (Pt, Pd and the like) coated on the DPF, was removed However, in the passive/active SDPF, the 2nd EM should be removed by an SCR catalyst coated on the DPF, but the SCR catalyst coated on the DPF is Zeolite type generally and has very low oxidation performance of the 2nd EM (CO, HC and the like) as compared with a precious metal catalyst.
FIG. 1 is a drawing representing the distribution of a conventional SDPF according to time. A filter material applied to a general SDPF includes SiC, AT, Cordierite and the like, and the porosity is between 55 and 65%. Further, the mean diameter of the pore is about 10˜25 μm. When it is applied to the SDPF, the distributions of the soot and the SCR catalyst are as shown in FIG. 1. The SCR catalyst is coated through a DPF inlet face to an outlet face because many SCR catalysts are coated on the porous DPF. This way, NOx is purified through the SCR reaction of NH3 and NOx on the SCR catalyst. However, the SCR catalyst can't sufficiently purify the 2nd EM generated when NH3 is produced by the post injection and the DPF is regenerated.
Therefore, when applying the SDPF, a technique reducing the 2nd EM optionally produced by the post injection is needed. When the SCR catalyst (Zeolite type) is coated on the wall side of the exhaust gas inlet of the porous DPF, and the precious metal catalyst is coated on the wall side of the exhaust gas outlet, the precious metal catalyst coated on the outlet face is coated to the wall side of the exhaust gas inlet, NH3 supplied to the wall side of the exhaust gas inlet is oxidized, and NH3+NOx=N2+H2O reaction is disturbed. Thus, when the precious metal catalyst is coated on the wall side of the exhaust gas outlet using a general coating method, there is a problem that it disturbs the SCR reaction of NH3+NOx and the NOx purification rate becomes low.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.